1. Field of the Invention
The present invention relates to a color picture tube, and more specifically to a color picture tube having a shadow mask structure composed of a number of grid wires, which constitute color selection or switching electrodes.
2. Description of Related Art
In a typical conventional shadow mask structure composed of a number of grid wires, which constitute color selection or switching electrodes for a color picture tube, the grid wires are stretched over a mask frame in the same direction, in parallel with one another.
In operation of the color picture tube, if the grid wires vibrate, or if the grid wires are shifted relative to one another proper color selection can no longer be obtained. In order to avoid this drawback, a damp wire is stretched over the grid wires to traverse the grid wires, and is contacted or fixed to the grid wires. With this arrangement, vibration and relative shifting of the grid wires are minimized or prevented. In ordinary cases, the damp wire is formed of a tungsten wire having a diameter of 20 .mu.m to 30 .mu.m.
In the above mentioned conventional mask structure, since the damp wires are formed of tungsten wire, when an electron beam passes through a spacing between each pair of adjacent grid wires, a portion of the electron beam directed toward a desired portion of a phosphor screen is blocked by the damp wire so that a corresponding portion of the phosphor screen does not emit light. In particular, in the case of a display signal for causing the whole of the phosphor screen to emit light, a black line appears in the display screen, and therefore, the display quality is inevitably deteriorated.